Railway signaling system



Oct. 5 19,43.l F; H. NICHOLSON ET AL. 2,331,134

RAILWAY S IGNALING SYSTEM Filed July 30, 1942 Patented Oct. 5, 1943RAILWAY SIGNALING SYSTEBI Frank H. Nicholson, Penn Township, AlleghenyCounty, and Crawford E. Staples, Pittsburgh, Pa., assignors to The UnionSwitch & Signal Company, Pennsylvania Swissvale, Pa.,

a corporation of Application July 30, 1942, Serial No. 452,894

13 Claims.

Our invention relates to railway signaling systems of the type employingcoded energy in the track circuits thereof.

In signaling systems of the type employing frequency code it iscustomary to employ energy of 75, 120 and 180 code frequency to providethree distinctive proceed indications. These are adequate for mostsituations, but in some cases it is desired to provide another or fourthproceed indication.

It is an object of this invention to provide improved means forproducing an additional indi cation in a coded signaling system.

A further object of the invention is to provide apparatus arranged sothat when locomotives equipped with cab signal apparatus arranged toprovidev three proceed indications are operated over stretches where thewayside apparatus is arranged to provide four proceed indications, thelocomotive cab signal equipment will operate at all times to provide anappropriate indication.

Another object of the invention is to provide a signaling system of thetype described which will not interfere with the operation of a lockouteircuit if such a circuit is employed.

Other objects of the invention and features of novelty will be apparentfrom the following description taken in connection with the accompanyingdrawing.

In practicing our invention we provide means for at times modifying theenergy of '75 code frequency by substantially reducing the length ofevery third oi period in the code and correspondingly increasing thelength of the succeeding on period. Means are provided to detect thisspecial code, including a slow release detector relay to which animpulse of energy is supplied on release of the track relay contacts andwhich has a release period such that it remains picked up during theshort off period but not throughout an ofi period of normal length. Inaddition, energy is supplied to this detector relay over a stick circuitif the relay is still picked up when the track relay contacts pick upagain. When the contacts of the track relay and of the slow releasedetector relay are picked up, a circuit is established to supply energyto a second slow release relay which is sufliciently slow acting toremain picked up during the intervals between the short off periods inthe modified code.

We shall describe one form of apparatus embodying our invention, andshall then point out the novel features thereof in claims.

In the drawing,

Fig. 1 is a diagram of a stretch of railroad track equipped with oneform of signaling apparatus embodying our invention, and

Fig. 2 is a diagram of the modified coded energy employed in the systemof this invention.

Referring to Fig. 1 of the drawing, there is shown therein a stretch ofrailroad track over which traffic normally moves in the directionindicated by the arrow, that is, from left to right. The track rails Iand 2 of the track stretch are divided by insulated joints 3 into tracksections for signaling purposes.

Electric current may be employed for propulsion purposes and where thisis so alternating current energy is employed in the track circuits, andimpedance bonds 4 of the customary form are provided to conduct thepropulsion current around each pair of insulated rail joints. As thedescription proceeds, however, it will be apparent that the apparatus ofthis invention is equally well suited for use on a steam road in whicheither direct or alternating current may be employed in the trackcircuits, while the impedance bonds may be omitted.

In addition, as impedance bonds are employed the signaling apparatusincludes means to check the insulated joints. As here shown, this meansis the non-cascading lockout circuit of United States Patent No.2,235,134 issued March 18, 194i, to Leslie R. Allison and Frank H.Nicholson. If our present invention is employed in a track stretch whereimpedance bonds are not required, the portions of the signalingapparatus relating to the lockout circuit may be omitted.

Similarly, the decoding means provided by this invention for detectingthe modified code is not limited to use in wayside apparatus but may beincorporated in cab signal apparatus foruse on locomotives.

In the diagram forming Fig. l of the drawing one complete section I2Tand parts of the two adjoining sections l IT and 13T, are shown. Each ofthese sections has located at the entrance end thereof a signal S forgoverning trafiic in the track stretch. The signais illustrated are ofthe familiar color light type and each signal has an upper and a lowerportion each of which has a green, a yellow and a red lamp. Theinvention, however, is not limited to the use of signals of this typeand any appropriate form of signal may be used. Likewise, the inventionis not limited to a system employing wayside signals, but is equallyapplicable to track stretches without waysidle signals and havingprovision for cab signals on y.

The rails of each track section form a part of stretch by a transmissionline, not shown. The

terminals of the power supply source are designated BX and CX, and itwill be assumed that the energy supplied from this source is alternatingcurrent of a frequency of 60 cycles per second.

The signaling system shown in Fig. 1 makes use of track circuit energycoded at four different y This coded energy is provided by frequencies.code transmitters CT which interrupt the supply circuits for theassociated track transformers a definite number of times per minuteaccording to traiiic or other conditions ahead. As'shown,.

each code transmitter is provided with four circuit making and breakingcontacts which are continuously actuated by a motor or other suitablemechanism. The rate of operation of the contacts l5, llEl and i8@ issuch as' to provide 75, 120 and 180 energy pulses per minute,respectively,y which are separated by, periods of equal duration inwhich no energy is supplied.

Each code transmitter has another contact designated M which is sooperated asv to produce two cycles of coded energy of 75 lcode frequencyin which the on and off periods are of approximately equal duration,while every third code cycle is modified in suchv manner that the-offperiod is much shorter than normal and the length of the on periodV iscorrespondingly increased. The pattern of this code is shown in Fig. 2.Since the distinguishing characteristic of the 75M code occurs in everythird code cycle of the 75 code, the '75M code is in eiect energyof 75code frequency modulated 25 times a minute.

The details of construction of the code transmitters to cause them toproduce the '75M code are not a part of this invention. However, thisspecial coded energy may be generated by cam wheels of suitable designsuch as those shown in United States Patent No. 1,861,488,V issued June'7, 1932 to Leslie A. Allison and Frank H. Nicholson. v

Each track circuit includes a code following track relay connectedacross the section rails at the entrance end of the section. As shown,the relay IZTR is of the direct current type and is connected to thetrack rails through a resonant rectier unit IZRU. e This unit includes atransformer, a capacitorv and a reactor so arranged and proportioned asto freely pass cycle signal control energy but so as not to passpropulsion current of a different frequency. The unit RU includes, inaddition, a rectifier which converts into direct current the alternatingcurrent supplied through the unit.

The track relay iZT?. has associated therewith auxiliary relays lZFSA,IPZBSA, IZHA, IZHB, 12K, |2J and l 2TRB, a decoding transformer IZDT,and a timing unit IZTU, while each of the other signals in the trackstretch has associated therewith equipment corresponding to thatassociated with signal IES. l

Each signal also has associated therewith a source of direct current,such as a storage battery, not shown, the terminals of which areydesignated B and C.

The equipment is shown in the condition which it assumes when the trackstretch is vacant.v At

such times energy of 180 code frequency is sup-' plied to the tracktransformer NTT by theeqilipment associated with section 13T. Theequipment for section IBT operates in the same manner as that forsection IZT.

The coded energy Supplied to track transformer l2TT feeds to the trackrelay ITR and produces code following operation of this relay. As aresult of operation of the relay EETR, energy is alternately supplied tothe two portions of the primary 2li of transformer IZDT from the directcurrent source. During the picked-up periods of the track relay contactsenergy is supplied from the transformer secondary winding 22 to thepick-up winding of the relay lEFSA over the circuit established by thetrack relay contact I6, while during the released periods of the trackrelay its contact i6 establishes a snubbing circuit for the relay IZFSAto keep the contacts of the latter relay picked up during the offperiods in the code.

When the track relay contacts are released, energy is supplied to therelay I2BSA over a circuit which includes back contact Il of the trackrelay and front contact 26 of the relay IZFSA, while contact 26 alsoconnects a snubbing resistor 28 across the terminals of the winding ofrelay IZBSA to make it slow in releasing.

At this time the relay IZHA is energized by current supplied over itsstick circuit which is traced from terminal B through its own frontcontact 29, front contact 3i) of relay ZBSA, winding of relay I2HA andback contact i6 of relay l ZTRB to terminal C. A resistor 32 isconnected across the terminals of the winding of relay IZHA to make therelay slow to release.

The relays IEK and I2J are energized from the decoding transformerthrough resonant units IZUDU andv lSDU, respectively, which includeinductances and capactances arranged and proportioned to permit energyto ilow freely through the units when the frequency of the currentsupplied thereto is that which is present when the track relay isresponding to energy of 120 and 180 code frequency, respectively, Vandto substantially prevent flow of energy at other times. 'Each of theseunits also includes arectier for rectifying the energy supplied throughthe unit. Y

As the track relay is responding to energy of 180 code frequency, energyis supplied through the unit ISEBDU to relay |2J and its contacts arepicked up. Accordingly, contact 32 of relay I2J interrupts the circuitthrough which energy is supplied to the timing u nit l2TU, and as aresult energy is not supplied from this unit to the relay IZTRB and itscontacts remain released so that the contacts 0f relay IEHB also remainreleased.

As relays I2HA and I2J are picked up, energy is suppliedyto the uppergreen lamp G of signal 52S over a circuit which includes front contact34 of relay IZHA and front contact 35 of relay IZJ, while energy issupplied to the lower red lamp R of this signal over a vcircuit whichincludes front contact 36 of relay i2I-IA and front contact 38 of relayl2J. Accordingly, the signal 12S displays a green over a red light whichis its clear or least restrictive indication.

At this timeenergy 0f 180 code frequency is supplied to tracktransformer HTT over a circuit which is traced from terminal BX throughcontact H of the code transmitter IZCT, front contact 40 of relay 12J,front Contact l2 of relay IZHA, front contact 1&3 of relay IZBSA, frontcontact 44 of relay I2FSA, and the primary winding of the track`transformer IITT to terminal CX. Accordingly, energy of code frequencyis supplied ,to the .rails of section l IT and the signal for thatsection is caused to display its clear indication.

When a train moving in the normal direction of trafficenters sectionI2T, the track relay I2TR is shunted and relay IZFSA releases so thatits contact 26 interrupts the supply of energy to relay IZBSA and alsointerrupts the snubbing circuit for this relay, with the result thatrelay I2BSA quickly releases. On release of relay IZBSA its contact 30interrupts the circuit of relay I2HA, while when the track relay ceasesto follow code, energy is no longer supplied to relay I2J and itscontacts release.

As a result of release of the relays IZHA and I2J, the circuit of theupper green lamp G of signal I2S is interrupted, and the upper red lampR is lighted by current supplied over back contact 34 of relay I2HA;also the vcircuit traced above for the lower red lamp R is interruptedand this lamp is lighted by energy supplied over back contact 36 ofrelay I2HA. The signal now displays a red lamp over a red lamp which isits stop or most restrictive indication.

At this time energy of "I5 code frequency is supplied to the tracktransformer IITT over a circuit which is traced from terminal BX throughback contact 43 of'relay IZBSA, back contact 44 of relay IZFSA, andcontact of the code transmitter I2CT.

When thetrain enters section I3T, the equipy ment for that sectionoperates in the same manner as the equipment for section I2T so thatsignal IBS provides its stop indication, while energy of '75 codefrequency is supplied to the track transformer I2TT.

When thev train Vacates section I2T, coded enorgy feeds to the trackrelay I2TR, and on the iirst movement of the track relay contacts totheir picked-up position an impulse of energy is supplied from thesecondary winding 22 of transformer I2DT to the pick-upv winding ofrelay IZFSA.

At this time the holding Winding of relay IZFSA is short circuited byback contact 2l of the relay so that the relay is slow to pick up. Therelay and transformer are proportioned so that the first impulse ofenergy supplied to the relay will not pick up the relay contacts.However, on the next or second picked-up period of the track relaycontacts the contacts of relay IZFSA pick up and contact 25 establishesthe circuit of the relay IZBSA so that on the next or second releasedperiod of the track relay contacts energy is supplied to the relay I2BSAand its contacts pick up.

On picking up of the track relay contacts after picking up of thecontacts of relay IZBSA energy issupplied to the relay I2HA over acircuit which is traced from terminal B through front contact I1 of thetrack relay, front Contact 3|] of relay IZBSA, winding of relay IZHA,and back contact 4S of relay IZTRB to terminal C. On picking up of thecontacts of relay IZHA its contact 29 establishes a circuit to maintainthe relay energized as long as the relay IZBSA is picked up and therelay I2TRB is released, while contact 29 of relay IZHA interrupts thecircuit for supplying energy to the holding winding of relay IZFSA.

On continued code following operation of the track relay energy issupplied to the relay IZFSA during the picked-up periods of the trackrelay and is supplied to the relay IZBSA during the released periods ofthe track relay. Accordingly, these relays are picked up and relay IZBSAmaintains the circuit of the relay IZHA.

On picking up of the contactsrof relay IZFSA its contact 44 interruptsthe circuit traced above for supplying energy of '15 code frequency totrack transformer I IT'I, and establishes a circuit including backcontact 43 of relay IZBSA for supplying steady uncoded energy to sectionI iT.

As explained in the patent to Allison and Nicholson referred to above,if the insulated joints separating sections IIT and I2T are defective,this steady energy will feed across the joints and prevent release ofthe track relay IZTR so energy is not supplied to relay IZBSA with theresult that relays IZBSA and IZHA remain released, while energy issupplied to the holding winding of relay IZFSA to keep its contactspicked up.

However, if the insulated joints are intact so that the steady energydoes not reach the track relay I2TR, the contacts of this relay willrelease at the end of the on period and cause energy to be supplied tothe relay IZBSA so that its coni tact 43 picks up vand interrupts thesupply of steady energy to track transformer I ITT. W hen the contactsof relay IZHA pick up, a circuit is established to supply energy of 75Mfrequency to track transformer IITT. This circuit is traced fromterminal BX through contact 15M of the code transmitter, back contact 48of relay IZHB, back contact 49 of relay I2K, back Contact 4i] of relayIZJ, front contact 42 of relay IEHA, front contact 43 of relay I2BSA,front contact 44 oi relay IZFSA, and primary winding of transformer IITT to transformer CX.

On the supply of this energy to section IIT the equipment for thatsection operates as hereinafter explained to control the signal for thatsection to cause it to display its advance approach indicationconsisting of a yellow over a yellow lamp.

Similarly, when the train vacates section HET the energy supplied tosection IET is changed from '75 to 75M code frequency and the relay ispicked up as hereinafter explained in detail and causes the signal I2Sto display its advance approach indication.

The construction of the timing unit IZTU is 5' not a part of ourinvention, but is shown and claimed in application Serial No. 452,9?12of Carl Volz, led July 30, 1942. This unit includes a transformer havinga primary winding which is energized in multiple with a condenser, whilethe secondary winding of the transformer is connected through arectifier'to the winding of relay i2TRB. The various parts of the unitare proportioned so that the energy supplied to the transformer primarywinding causes the transformer core to be saturated, while oninterruption of the supply of energy to the transformer primary winding,this winding and the condenser associated therewith form a highly dampedoscillating circuit. The energy circulating in the transformer primarywinding causes energy to be induced in the transformer secondary windingfrom. which it is supplied through the rectifier to the relay IZTRB. Thecharacteristics of the timingr unit and of the relay IZTRB are such thaton interruption of the supply of energy to the timing unit, energy issupplied therefrom to the relay IZ'I'RB which'isl eifective to cause thecontacts of relay IZTRB to pick up and to remain picked up for a timelonger than the short off period in the '75M code but not as long as theoff eriods .in the 75 code.

When the track relay I2TR is responding to energy of '75 code frequency,energy is supplied to the primary winding of the transformer of thetiming unit I2TU over the circuit which is traced from terminal B c1 thesource through iront con@ tact l of the track relay IZTR, asymmetricunit 5l, front contact 52 of relayv ItIZBSA, back Contact. S2 of relayZJ, back contact 53 cui' relay MK. back contact ll of relay i-ZTRB,and'priinary winding of the timing unit. transformer to terminal C.

On movement of the track relay Contactate, their released positions thesupply of energy toj the timing unit transformer is interrupted andthisA imit operates as explained` above tosupply energy through the.rectifier incorporated; in the unit to therelay EZTRB over the circuitwhich is traced from the positive output terminal or the rectier overback contact 5E. of track relay SETR, and winding ofrelay ltd-RB toterminal C, it being noted that the other output terminalof therectilier is connected to termin-al O. The energy supplied to thewinding of relay iTRB' causes the contacts` of this.v relay topick upand to remain picked up for a short time interval. However, asexplained'ahove, this time interval is shorter than the olf periods inthe 'i5' code. so that when the track relay is respond-ing to energy oi75 code frequency the contacts of' relay lTRB release before the trackrelay contacts pick up again, and as a result contact 54 of relaylf2-TRB establishes the circuit for rsupplying energy to the unit IZTUon subsequent picking up of the track relay contacts. In addition,Contact 5S or" relay lZTRB is releasedl and interruptsthe circuit ofrelay itl-EB so that this relay remains released at this time, and itscontact te maintains the circuit of the lower red lamp R of signal VES,while its contact lt'maintains the circuit for supplying energy of 75Mcode frequency to section IlT. n

On picking up of relay lZTRB its contact 46 interrupts the circuit ofrelay lilla, but this relay is suflicientlyV slow in releasing to remainpicked up during the picked-up periodsr of con'- tact 46.

As the circuit oi relay IZHA includes a back contact Il@ of relayIZTRB', the relay I2HA will be released ii the contacts of lrelayl-ZTRBremain picked up for any reason. This arrangement checks the relayIQTRB to insure that it releases, and, therefore, permitsthe use of' arelay having metal to metal contacts for this purpose.

When the train advances far enough to vacate section IST, energy of 75code frequency feeds to the track relay for that section so that signal53S displays its approach indication, while energy of 75M code frequencyis supplied to section VET. On the supply of this energy to the trackrelay HTR it continues to follow code in such manner that the relaysI,2FSA,.I2BSA and, S21-IA are maintained energized. As. explained above,each time the track relay contacts release the contacts of relay lZTRB`pick up, While when a short olf period in the '25M code is encountered,the contacts of the. track relay pickup. before the contacts of relaylZTRBrelease. v When this occurs, energy is supplied to relay LZTRB overa circuit which is traced from terminal B through front contact l5 oftrack relay IETR, asymmetric unit 5l, front contact 52 of relay I'ZBSA,back Contact 32 of relay 12J, back contact. 53 ot rel-aylEK, frontcontact 54 of relay I2TRB andv wind'- ing of relay IZTRB to terminal C.This energy,

keeps the contacts of relay lZTltB. pickedl up throughout the long onperiodI in the '15M code followingy the short 01T period.

In; addition. on. picking up: of the. track relay contacts. while thecontacts of relay l-ZTRB are still picked up, the relays 52E-TB andlZBSA are energized in series. over a. circuit'which is traced fromterminal B through front. contact l5 cf .relay liZTR, asymmetric unitel, front Contact 52 of relay l'llBSA, back contact, 32 or"- relay E25,back contactl of relay 12K, iront contact 5d of relay Iii-TRB, frontcontact 5%y of relay lfTR,

winding of relay 12T-IB, iront Contact 53 of relay IZTRB, front contactZitv of relay IEFSA, and winding of relay l2BSA to terminal C. Theenergy supplied to the relay IZBSA over this circuit insures that thecontacts of relay IZBSA will remain picked up throughout the long onperiod in the 75M code, While the energy supplied to the relay llt-HB atthis time causes the relay contacts to pick up. The relay IZHB is of atype the contacts of which are slow in releasing and when the relayisenergized throughout the long on period in the '75M code, the flux inthe relay core isbuilt upto a value such that the relay contacts wil-l.remain pickedupduri-ng the intervals between the long on periods in the75M code.

On picking up of the contacts' of relay Lil-.iB its contact 48interrupts the circ-uit traced above for supplying energyl of 75M codefrequency to track transformer ll TT, and establishes a circuit forsupplying energy of v code frequency thereto. This circuit is tracedfrom terminaly BX through contact l2@ of the code transmitter, frontcontact 5.8 of relay l-2HB, back Contact t9 of relay 52K, back contactill of relay 12J, iront contact l2 ci relayr'i2I-IA, front contact 6301"relay IZBSA, front Contact M of relay lZFSA, and' primary winding of thetrack transformer NTT to terminal CX.

4When relay IZHB picks up,l its contact 5t interrupts the previouslytraced circuit for supplying energy to the lower red lamp. R; of signal42S and establishes a circuit for supplying energy to the lower yellowlamp Y of this signal. This circuit is traced from terminal B throughfront contact 3.6 oi relay WHA, back contact 38 of relay lZJ, backcontact 6l of relay 12K, front contact 6l! of relay lZHB, andjlamp Y toterminal C.V Accordingly,r the signal l2S displays its advance approachindication consisting of a yellow. lamp over a yellow lamp.

On release of the track relay lZTR after the long on period in the 75Mcode its contact l5 interrupts the supply of energy to the relays I2TRB,IZHB, and IZBSA and the relay EQTRB releases. The contacts ofY relayIZHB are maintained picked up because ofthe slow releasingcharacteristic of the relay, while on release of the track relay I 2TH.its contact Il establishes the previously traced circuit for supplyingenergy to the relay l ZBSA so its contacts remain picked up.

In addition, on release of relay l-Tli its contact 55A interrupts thepreviously traced circuit for energizing the relays lill-IB' and lBSA inseries and establishes the circuit to permit energy 4to be supplied fromthe timing unit 92TH to the lished by back. contact 56 of thel trackrelay lZTR i and the contacts of relay I2TRB remain released.

On the first picked-up period of the track relay contacts after the longon period in the 75M code energy is supplied to the primary winding ofthe transformer incorporated in the timing unit IZTU over the circuitincluding back contact 54 of relay IZTRB so that on the next releasedperiod of the track relay contacts the timing unit I2TU operates asexplained above to supply energy to the relay I2TRB and its contactsbecome picked up. However, the ofi period in the 75M code at this timeis lonc`.,.` than the release period of the contacts of relay IZTRB sothat its contacts release before the track relay contacts pick up again.Accordingly, energy is not supplied to `the relay I2HB at this time.

On the next or second picked-up period of the track relay contactssubsequent to the long on period energy is again supplied to the timingunit I2TU, while on the next released period of the track relaycontacts, which occurs during a short off period in the 75M code, energyis again supplied from the timing unit I2TU to the relay IZTRB and itscontacts pick up with the result that on picking up of the track relaycontacts the contacts of relay IZTRB are still picked up so that energyis supplied over the holding circuit for relay IZTRB, and is alsosupplied to the relays IZHB and I 2BSA in series.

It will be seen, therefore, that when the track relay is responding toenergy of 75M code frequency and the short off period in the code isencountered, the track relay contacts pick up before the contacts ofrelay IZ'I'RB release, and

as a result energy is supplied to relay IZTRB to maintain its contactspicked up during the long on period which follows the short off period.In addition, energy is supplied to the relay I2HB to pick up itscontacts and to maintain them picked up during the time intervalsbetween the long "on periods in the code, while energy is supplied tothe relay I2BSA to maintain its contacts picked up during the long onperiod in this code. relay IZ'I'R responds to energy of 75M codefrequency the contacts of relay lZHB are maintained picked up.

When the train advances far enough to vacate the section in advance ofsection IST, energy of 75M code frequency is supplied to section IST andthe equipment for that section operates as explained above in connectionwith section I2T to cause energy of 120 code frequency to be supplied tothe rails of section I2T. When the track relay IZTR responds to thisenergy, the frequency of the current induced in the secondary winding 23of decoding transformer IZDT is such that it is freely passed byresonant unit I20DU and the re- Accordingly, as long as the track layIZK picks up so that contact 53 interrupts the circuit for supplyingenergy to the timing unit I2TU, and for supp ying energy to relay IZTRBand to relays IZHB and IZBSA in series. v

Accordingly, relays IZTRB and IZHB thereafter remain released.

On picking up of the relay I2K its Contact SI interrupts the circuittraced above for supplying energy to the lower yellow lamp Y of signalIZS and establishes a circuit including front contact 35 of relay IZHA,back Contact 38 of relay IZJ,

and front contact 6I of relay I2K for supplying energy to the lowergreen lamp G of signal |255. The signal I2S, therefore, displays itsapproach medium indication consisting of a yellow lanp over a greenlamp.

When the relay I2K picks up, its contact 49 interrupts the circuittraced above for supplying energy of 120 code frequency to transformer II TT and establishes a circuit for supplyingf energy of 180 codefrequency thereto. This circuit is traced from terminal BX throughcontact I8!) of the code transmitter I2CT, front contact 49 of relayI2K, back contact 4D of relay I2J, and front contacts of the relaysIZHA, IZBSA and IZFSA to the transformer IIT'I.

When the train advances far enough to vacate two sections in advance ofsection IST, energy of 120 code frequency is supplied thereto and theequipment for that section operates to supply energy of 180 codefrequency to track transformer IZTT. When this energy feeds to the trackrelay I2TR, the frequency of the energy induced in transformer secondarywinding 23 is such that it is no longer passed by the resonant unitIZGDU, but is freely passed by the unit lSDU so that relay IZK releasesand relay I2J picks up. On picking up of relay I2J its contact 32interrupts the circuit of the timing unit IZTU, and of the relays ITRB,IHB, and I ZBSA, while its contacts 38 interrupts the circuit tracedabove for supplying energy to the lower green lamp G and establishes thecircuit including front contact 38 of relay IEHA for supplying energy tothe lower red lamp R of signal I2S. In addition, at this time contact S5of relay I2J interrupts the circuit of the upper yellow lamp Y of signalIZS and establishes the circuit including front contact 34 of relay IZHAfor supplying energy to the upper green lamp G of signal I2S,Accordingly, vthe signal IES displays its clear indication consisting ofa green lamp over a red lamp.

On picking up of relay IZJ contact 49 interrupts the previously tracedcircuit for supplying energy of 186 code frequency to transformer II'I'Iand establishes another circuit for supplying energy of this codefrequency to the transformer IITT.

From the foregoing it will be seen that the system of this inventionoperates to provide four distinct proceed indications. rihree of theseindications are provided by the usual coded energy of '75, 120 and 180code frequencies, while one of these indications is provided by thespecial '75M code which is a modification of the standard '75 code.

It has been found that when locomotives construction and having decodingmeans for detecting energy of 75, 120 and 180 code frequency areoperated in sections supplied with the special 75M code, the cab 'signalapparatus gives the same response to the '75M code as it gives whensupplied with energy of 75 code frequency. Accordingly, when alocomotive equipped with standard four indication cab signal apparatusis operated in a track stretch equipped with the ve indication apparatusprovided by this invention, the cab signal equipment will provide itsapproach indication through the two blocks in the rear of an occupiedblock. In such situations the wayside signal at the entrance to thesecond section in the rear of an occupied block will display itsadvanceapproach indication, while when the locomotive enters this section, thecab signal will provide its approach indication.

If desired, the locomotive cab signal apparatus may include means fordetecting the special 75M code, and if this is done, the cab signal willprovide its advance approach indication when the locomotive is in asection to which energy of 75M code frequency is supplied.

Operation of equipment when an insulated .'ioint is defective' if theinsulated joints separating two sections are defective.

lf a train breaks down one of the insulated joints 3 separating sectionsIIT and IZT, energy of 75 code frequency supplied to transformer l ITTmay pick up the track relay I2TR when the train advances far enough forthe rear of the train to be located some distance in advance of thetrack relay.

On initial movement of the track relay contacts to their picked-uppositions an impulse of energy is supplied through the decodingtransformer iZDT to the pick-up winding of relay IZFSA, but the contactsof this relay remain released and maintain the supply of energy of 75code frequency to the transformer IITT, while they interrupt the circuitof relay iZBSA. At this time contact 52 of relay I2BSA is released andprevents the supply of energy through the asymmetric unit 5I to thetiming unit I-ZTU. As relay IZFSA remains released energy is notsupplied to the relay IZBSA on release of the track relay.

On the next or second movement of the track relay contacts to theirpicked-up positions another impulse of energy'is supplied to the pick-upWinding of relay SEF-SA and its contacts pick up with the result thatcontact 44 interrupts the oircuit for supplying energy of '75 codefrequency to the transformer IiTT and establishes the circuit includingback contact is of relay IZBSA for supplying steady uncoded energy tothe transformer IITT. This energy feeds across the defective joints andkeeps the track relay contacts picked up.

As the track relay contacts and the contacts of relay IEFSA are pickedup, energy is supplied to the holding Winding of relay IZFSA over thecircuit Which is traced from terminal B through front contact Il of thetrack relay, back contact 2Q of relay I lfHA, front contact 2'! of relayIEFSA, and holding Winding of the relay IZFSA to terminal C. The energysupplied to the holding winding of relay IZFSA keeps the relay contactspicked up so that its contact 2l maintains the circuit of the relayholding Winding, While its contact it maintains the circuit forsupplying steady energy to the transformer IITT. This energy feedsacross the defective joints and keeps the track relay contacts picked upwith the result that energy is not supplied to the relay IZBSA and itscontacts remain released and interrupt the circuit `of relay IZHA sothat relay IZHA remains released and causes signal I2S to continue todisplay its stop indication.

If an insulated joint separating sections IIT and 52T breaks down whensection 12T is vacant, the coded energy feeding from transformer I ITTacross the defective joint to track relay I ZTR combines with energysupplied from transformer $2TT to the track relay IZ'TR. If at the timethe insulated joint becomes defective the impulses of coded energysupplied to transformersV I ITT and NTT are out of step, the contacts oftrack relay I2TR Will be held picked up an abnormally large proportionof the time. If at the time the insulated joint becomes defective theimpulses of coded .energy supplied to the transformers IiTT and I2TT arein step, they Will soon become out of step as the code transmitterscontrolling the supply of energy to the two sections are operated byinduction motors and these Will not run at exactly the samC` speed forany substantial period of time.

As a result of the increase in the picked-up periods of the track relaycontacts, the circuit of the relay IZBSA is interrupted so much of thetime that this relay will release with the result that its contact i3interrupts the circuit for supplying coded energy to the transformer IITT and establishes a circuit to supply steady energy thereto. Thisenergy feeds across the defective joint and keeps the track relaycontacts picked up so that energy is no longer supplied through thedecoding transformer I2DT to the relay iFSA, nor to the relay IZK orI2J, so that these relays release.

In addition, on release of relay IEBSA its contact 3U interrupts thecircuit of relay ill-IA and the contacts of this relay release, butbecause of the slow releasing characteristic of this relay its contact29 remains picked up and interrupts the circuit for supplying energy tothe holding Winding of relay 'l EFSA until after contact 2 of relayIZFSA has released and interrupted this circuit.

On release of relay IZBSA its contact 52 interrupts the circuit forsupplying energy to the timing unit IZTU, and also to relays iTRB, IZHBand I'BSA.

On release of relay IEFSA its contact liLl interrupts the supply ofsteady energy to transformer IITT and causes energy of 75 code frequencyto be supplied thereto over the circuit which is traced from terminal BXthrough back Contact 43 of relay IZBSA, back contact 4d of relay IZFSA,and Contact 'i5 of the code transmitter IECT to the transformer IITT.Energy from the transformer feeds across the defective joint to trackrelay I2TR and combines With the energy supplied from transformer IZTT.

The impulses of coded energy supplied to the track relay I2TR from thetransformers IITT and I2TT will cause the contacts of the track relay tobe picked up most of the time, but a time will soon be reached When therelationship of the two codes is such that the track relay contac'tswill pick up twice in rapid succession. When 55'tained picked up. Inaddition, on picking up of this occurs, the relay IEFSA Will pick up andits contact 21 will establish the circuit traced above for supplyingenergy to the relay holding Winding so that the relay contacts arethereafter mainthe relay IZFSA its contact it interrupts the circuit forsupplying energy of 'l5 code frequency to transformer I ITT andestablishes the circuit for supplying steady energy thereto. This energykeeps the track relay IZTR` picked up so that energy is not supplied Vtorelay IZBSA. Accordlingly, the contacts of relay i2BSA remain redecodingmeans, and if a locomotive equipped with existing cab signal apparatusis operated in a section to which the modified coded energy is suppliedthe locomotive cab signal apparatus will operate to provide a suitableproceed indication.

Furthermore, it has been found that energy of the code pattern employedfor the '7 5M code frequency has a minimum effect on the decoding unitsfor energy of 120 and 180 code frequency.

It will be seen also that the decoding means for detecting the energy of'llcode frequency is arranged so that it does not interfere with thelockout circuit. The relay BSA has a release time just long enough tobridge the picked-up periods of the track relay when the track relay issupplied with energy of 75 code frequency so that this relay willrelease quickly and establish the lockout circuit if energy feeds acrossa defective joint and keeps the track relay picked up an abnormallylarge proportion of the time. The decoding means for the '75M codefrequency includes means for supplying energy to the relay ESA duringthe long on periods in this code to thereby prevent release of thisrelay at such times and resultant interference with the supply of energyto the adjacent section in the rear. This means for supplying energy tothe relay BSA is effective only during the long on periods in the 75Mcode so that there is a minimum of interference with the release of therelay BSA.

In addition, the 75M decoding means is controlled by the relays whichdetect the other code frequencies so that the '75M decoding means isprevented from functioning if the relays which detect energy of 120 and180 code frequency are picked up. This reduces the period of operationof the 75M decoding means, while it prevents operation of this means inresponse to momentary release of the track relay contacts occurring whenthe track relay starts to follow code, when there is a change in thefrequency of the energy supplied to the track relay, or when the trackrelay is supplied with energy of 120 or 180 code frequency- Similarly,the decoding means for the 75M code is controlled by the relay BSA sothat this decoding means will function only when the track relay isresponding to coded energy.

The modified code employed in this system and the decoding means forthis code are of such nature that coded energy resulting frommodications of the standard code due to track circuit or otherconditions will not operate this decoding means. The short off period inthe 75M code must be present to cause the contacts of the track In themodified code employed in this system the short off period is followedby a long on period and energy is supplied to the relay HB throughoutthis long on period so that enough energy is supplied to the relay tokeep it picked up during the interval between the long on periods. Theselong on periods are substantially longer than the "on periods present inany of the standard codes and will not be produced by modifications 0fthose codes by track circuit conditions.

In addition, the special code employed in this system is arranged sothat the modified code cycles are of the same length as the code cyclesof standard pattern, and the code can be generated by existing types ofmotor driven code transmitters with only a slight modification thereofconsisting of the addition of another cam.

Although We have herein shown and described only one form of apparatusembodying our invention, it is understood that various changes andmodifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

1. In a coded signaling system, combination, a code following relay,means for at times supplying to said relay recurring cycles of codedenergy, each of said cycles consisting of two periods of substantiallyequal length, one of said periods being an on period during which energyis supplied to said relay and the other of said periods being an offperiod during which no energy is supplied, means for at times period-Aically modifying the cycles of coded energy supplied to said relay bysubstantially reducing the length of a predetermined one of the periodsof said code cycle, a first relay responsive to op eration of said codefollowing relay by either normal or modified coded energy, an auxiliaryrelay, means operative on response of said code following relay to saidpredetermined code periods to supply to said auxiliary relay energyeffective to pick up the contacts of said auxiliary relay and tomaintain them picked up for a time longer than a period of reducedlength but not as long as a period of normal length, a circuit includinga front contact of said auxiliary relai.T and a contact of said codefollowing relay closed on response of said relay to said other codeperiods for supplying energy to a second relay, and signaling meansgoverned by said rst and sccond relays.

2. In a coded signaling system, in combination, a code following relay,means for at times supplying to said relay recurrinor cycles of codedenergy, each of said cycles consisting of two periods of substantiallyequal length, one of said periods being an on period during which energyis supplied to said relay and the other of said periods being an offperiod during which no energy is supplied, means for at timesperiodically modifying the cycles of coded energy supplied to said relayby substantially reducing the length of a predetermined one of theperiods of said code cycle, a first relay responsive to operation ofsaid code following relay by either normal or modified coded energy, anauxiliary relay, means operative on response of said code followingrelay to said predetermined code periods to supply to said auxiliaryrelay energy effective to pick up the contacts of said auxiliary relayand to maintain them picked up for a time longer than a period ofreduced length but not as long as a period of normal length, a circuitincluding a front contact of said auxiliary relay and a contact of saidcode following relay closed on response of said relay to said other codeperiods for also supplying energy to said auxiliary relay, and signalingmeans governed by said code following relay and said auxiliary relay andby said rst relay.

3. In a coded signaling system, in combination, a code following relay,means for at times supplying to said relay recurring cycles of codedenergy,` each of said cycles consisting oftwo periods of substantiallyequal length, one of said periods being an on period during which energyis supplied to said relay and the other of said periods being an offperiod during which no energy is supplied, means for at timesperiodically modifying the cycles of coded energy supplied to said relayby substantially reducing the length of a predetermined one of theperiods of said code cycle, a rst relay responsive to operation 'cf saidcode following relay by either normal or modified coded energy, anauxiliary relay, means operative on response of said'code followingrelay to said predetermined -code periods to supply to said auxiliaryrelay energy effective to pick up the contacts of said auxiliary relayand to maintain them picked up for a time longer than a period ofreduced length but not as long as a period of normal length, a slowreleasing relay, a circuit including a front contact of said auxiliaryrelay and a contact of said code following relay closed on response ofsaid relay to said other code periods for supplying energy to said slowreleasing relay and for also supplying energy to said auxiliary relay,and signaling means governed by said first relay and by said slowreleasing relay.

4. In a coded signaling system, in combination, a code following relay,means for at times supplying to said relay recurring cycles of codedenergy, each of said cycles consisting of two periods of substantiallyequal length, one of said periods being an on period during which energyis supplied to saidV relay and the other of said periods being an offperiod during which no energy is supplied, means for at timesperiodically modifying the cycles of coded energy supplied to said relayby substantially reducing the length of a predetermined one of theperiods of said code cycle and correspondingly increasing the length ofthe other period of said code cycle, a first relay responsive tooperation of said code following relay by either normal or modied codedenergy, an auxiliary relay, means operative on response of said codefollowing relay to said predetermined code periods to supply to saidauxiliary relay energy eiective to pick up the contacts of saidauxiliary relay and to maintain them picked up for a time longer than aperiod of reduced length but not as long as a period of normal length, acircuit including a front contact of said auxiliary relay and a contactof said code following relay closed on response of said relay to saidother code periods for supplying energy to a second relay, and signalingmeans governed by said first and second relays.

5. In a coded signaling system, in combination, a code followingrelay,means for at times supplying to said relay recurring cycles of codedenergy, each of said cycles consisting of two periods of substantiallyequal length, one of said periods being an on period during which energyis supplied to said relay and the other of said periods being an oiperiod during which no energy is supplied, means for at timesperiodically modifying the cycles of coded energy supplied to said relayby substantially reducing the length of a predetermined one of theperiods of said code cycle and correspondingly increasing the length ofthe other period of said code cycle, a rst relay responsive to operationof said code following relay by either normal or modied coded energy, anauxiliary relay, means operative on response of said codefollowing'relay to said predetermined code periods to supply to saidauxiliary relay energy effective to pick up the contacts of saidauxiliary relay and to maintain them picked up for a time longer than aperiod of reduced length but not as long as a period of normal length acircuit including a front contact of said auxiliary relay and a contactof said code following relay closed on response of said relay to saidother code periods for also supplying energy to said auxiliary relay,and signaling means governed bysaid code following relay and saidauxiliary relay and by said first relay.

6. In a coded signaling system, in combination, a code following relay,means for at times supplying to said relay recurring cycles of codedenergy, each of said cycles consisting of two periods of substantiallyequal length, one of said periods being an on period during which energyis supplied to said relay and the other of said periods being an offperiod during which no energy is supplied, means for at timesperivodically modifying the cycles of coded energy supplied to saidrelay by substantially reducing the length of a predetermined one of theperiods of said code cycle and correspondingly increasing the length ofthe other period of said code cycle, a rst relay responsive to operationof said code following relay by either normal or modiiied coded energy,an lauxiliary relay, means operative on response of said code followingrelay to said predetermined code periods to supply to said auxiliaryrelay energy elective to pick up the contacts of said auxiliary relayand to maintain them picked up for a time longer than a period ofreduced length but not as long as a period of normal length, a slowreleasing relay, a circuit including a front contact of said auxiliaryrelay and a contact of said code following relay closed on response Vofsaid relay to said other code periods for supplying energy to said slowreleasing relay, and signaling means governed by iirst relay and by saidslow releasing relay.

7. In a coded signaling system, in combination, a code Yfollowing relay,means for at times supplying to said relay recurring cycles of codedenergy, each of said cycles consisting of two periods of substantiallyequal length, one of said periods being an on period during which energyis supplied to said relay and the other of said periods being an oifperiod during which no energy is supplied, means for at timesperiodically modifying the cycles of coded energy supplied to said relayby substantially reducing the length of a predetermined one of theperiods of said code cycle and correspondingly increasing the length ofthe other period of said code cycle, a rst relay responsive to operationof said code following relay by either normal or modified coded energy,an auxiliary relay, means operative on response of said code followingrelay to said predetermined `code periods to supply to said auxiliaryrelay energy effective to pick up the contacts of said auxiliary relayand to maintain them picked up for a time longer than a period ofreduced length but not as long as a period of normal length, a slowreleasing relay, a circuit including a front contact of said auxiliaryrelay and a contact of said code following relay closed on response ofsaid relay to said other code periods for supplying energy to said slowreleasing relay and for also supplying energy to auxiliary relay, andsignaling means governed by said rst relay and by said slow releasingrelay.

8. In a coded signaling system, in combination, a code following relay,means for supplying to said relay coded energy consisting of alternateonl and off periods of substantially equal duration, means for at timesperiodically modifying the coded energy supplied to said relay bysubstantially reducing the length of an on period and correspondinglyincreasing the length of the succeeding on period, a first relayresponsive to operation of said code following relay by either normal ormodified coded energy, an auxiliary relay, means operative on release ofthe contacts of said code following relay to supply to said auxiliaryrelay energy effective to pickup the contacts of said auxiliary relayand to maintain them picked up for a. time longer than an oi period ofreduced length but'shorter than an off period of normal length, acircuit including front contacts of said code following relay and ofsaid auxiliary relay for supplying energy to said auxiliary relay, asecond relay governed by said code following relay and said auxiliaryrelay, and signaling means controlled by said first and second relays.

9. In a coded signaling system, in combination, a code following relay,means for supplying to said relay coded energy consisting of alternateon and off periods of substantially equal duration, means for at timesperiodically modifying the coded energy supplied to said relay bysubstantially reducing the length of an ofi period and correspondinglyincreasing the length of the succeeding on period, a first relayresponsive to operation of said code following relay by either normal ormodified coded energy, an auxiliary relay, means operative on releaseoi" 'the contacts of said code following relay to supply to saidauxiliary relay energy eiiective to pick up the `contacts of saidauxiliary relay and to maintain them picked up for a time longer than an01T period vof reduced length but shorter than an oif period of normallength, a circuit including front contacts of said code following relayand of said auxiliary-relay for supplying energy to said auxiliaryrelay, a slow releasing relay, a circuit including front contacts ofsaid code following relay and of said auxiliary relay for supplyingenergy to said slow releasing relay, and signaling means governed bysaid first relay and by said slow releasing relay.

10. In a coded railway signaling system, in combination, a stretch ofrailway track over which traine normally moves in one direction, therails of said section being divided by insulated joints into a forwardand a rearward section, a, code following track relay at the entranceend of the forward section and having a winding receiving energy overthe rails of said section, means at the exit end of said forward sectionfor supplying to the rails of said section coded energy consisting ofalternate on and ofi periods of substantially equal duration, means forat times periodically modifying the coded energy supplied to saidsection by substantially reducing the length of an off period andcorrespondingly increasing the length of the succeeding on period, meansincluding a from; contact of said track relay for supplying energy to afirst auxiliary relay, means including a back contact of the track relayand a front contact of said first auxiliary relay for supplying energyto a second auxiliary relay, said second auxiliary relay being slowenough in releasing to remain picked up for a period approximately aslong as an on period of normal length after the supply of energy theretois interrupted, means for supplying coded energy to the rails of saidrearward section, a circuit complete when the contacts of the firstauxiliary relay are picked up and the contacts of the second auxiliaryrelay are rreleased and over which steady energy may be supplied to therails of said rearward section, means operative on release of thecontacts of the track relay to supply to a third auxiliary relay energyeffective to pick up the contacts of said relay and to maintain thempicked up for a time longer than an oil period of reduced length butshorter than an off period of normal length, a circuit including frontcontacts of said track relay and of said third auxiliary relay for alsosupplying energy to said third auxiliary relay, a circuit includingfront contacts of said track relay and said third auxiliary relay vforsupplying energy to said second auxiliary relay, and means governed bysaid third auxiliary relay for supplying coded energy to the rails .ofsaid rearward section.

11. In a coded'railway signaling system, in combination, a stretch ofrailway track over which traffic normally moves in one direction, therails of said section being divided by insulated joints into a forwardand a rearward section, a code following track relay at the entrance endof the forward section and having a winding receiving energy over therails of said section, means at the exit end of said forward section forsupplying to the rails of said section coded energy consisting ofalternate on and off periods of substantially equal duration, means forat times periodically modifyingthe coded energy supplied to saidsectionV by substantially reducing the length of an oii period andcorrespondingly increasing the length of the succeeding on period, meansincluding a front contact of said track relay for supplying energy to afirst auxiliary relay, means including a back contact of the track relayand a front contact of said first auxiliary relayfor supplying energy toa second auxiliary relay, said second auxiliaryrelay being slow enoughin releasing to remain picked up for a period approximately as long asan on period Hof normal length after the supply of energy thereto isinterrupted, means for supplying coded energy to the rails of saidrearward section, a circuit complete when the contacts of the firstauxiliary relay are picked up and the contacts of the second auxiliaryrelay are released and over which steady energy may be supplied to therails of said rearward section, means operative on release of thecontacts of the track relay to supply to a third auxiliary relay energyeffective to pick up the contacts of said relay and to maintain thempicked up for a time longer than an oli period of reduced length butshorter than an off period of normal length, means effective when thecontacts of said track relay and said third auxiliary relay are pickedup to supply energy to said third auxiliary relay, to said secondauxiliary relay, and to a slow releasing relay, and means governed bysaid slow releasing relay for supplying coded energy to the rails ofsaid rearward section.

l2. In a coded railway signaling system, in combination, a stretch ofrailway track over which trame normally moves in one direction, therails of said section being divided by insulated joints into a forwardand a rearward section, a code following track relay at the entrance endof the forward section and having a winding receiving energy over therails of said section, means at the exit end 0f said forward section forsupplying to the rails of said section coded energy consisting ofalternate on and off periods of substantially equal duration, means forat times periodically modifying the coded energyA the track relay and afront contact of said-first I auxiliary relay for supplying energy to asecond auxiliary relay, said second auxiliary relay being slow enough inreleasing to remain picked up for a period approximately as long as anon period of normal length after the supply of energy thereto isinterrupted, means for supplying Coded energy to the rails of saidrearward section, acircuit complete when the contacts of the rstauxiliary relay are picked up and the contacts of the second auxiliaryrelayare releasedvand over which steady energy may be supplied to therails of said 'rearward section, means operative on release. of thecontacts of the track relay to supply to a third auxiliary relay energyefectiveI to pick uptheV ,contacts of said relay and to maintain thempicked up for a time longer than an oi period of reduced length butshorter than an off .period of normal length, means eiective when thecontacts of the track relay and of .the third auxiliary relay are.picked up to supply energy to 'said' third auxiliary Vrelay/and to aslow releasfingrelay, meansl effective when the contacts of the trackrelay and of said third auxiliary relay are picked up to prolong thepicked-up periods of the contacts of` the second auxiliary relay, and

.means governed bysa'id slowreleasing relay for :supplying energy to therails of said rearward section. 13. In a coded railway signaling system,in combination, a stretch of railway track lover -'Which traffic.normally moves inl one direction,

the rails of said section being divided by insulated joints into aforward and a Irearward section, a code following track relay at theentrance end of the forward section and having a winding receivingenergy over the rails of said section, means at the exit end of saidforward section for supplying to the rails of said section coded energyconsisting of alternate. .on and on periods of substantially equalduration, 'means for at times periodically modifying the `c'oded'errergysupplied to said section by substantially ree ducing the length of anoiperiod 'and correspondingly increasing the length of the'succeeding onperiod,`means including a front contact of said track relayfor-supplying energy to a rst auxiliary relay, lmeans including a backcontact of the track relay and afront contact or said'rst auxiliaryrelay for supplying energy to a second auxiliary relay, said secondauxiliary relay being ,slow enough in releasing to remain picked up fora period approximately as long `as an on period of normal length afterthe supply of energy thereto is interrupted, means for supplying codedenergy to the rails of said rearward section, a circuit complete whenthe contacts of the first auxiliary relay are picked up and the contactsof the second auxiliary relay are released and over which steady energymay be supplied to the rails of said rearward section, means operativeon release of the contacts `of the track relay provided the contactsofthe second auxiliary re lay are picked up to supplyto a thirdauxiliary relay energy effective to pick up the'contacts of said relayand to maintain them picked up for a time longer than an oir period lofreduced length but shorter than an oli period of normal length, meanseffective when the contacts oi the track relay and of said second andthird auxiliary relays are picked up to supply energy to said thirdauxiliary relay and to a slowreleasing relay, and means governed by saidslow releasing relay for supplying coded energy to said rearwardsection. 1

n, H. NICHOLSON. "CRAWFORD E. STAPLES.

